I think it is time to move on from the agent. At no point should you feel that you are bothering them. I am a "fill service" agent but I'm not going to knock any other business model. My clients are very satisfied with how I work and what I earn.
It seems that you have a unique property that is requiring a innovative marketing situation and has some specific drawbacks also with the assessments. I think that it is going to be more difficult than just puttin it on the web and posting a few flyers around.
The best post in this is Deborah's. You need an agent that understands the motivations of the potential buyer and how to get them to notice the availibility and then to present it as the best option for them.